1) Field of the Invention
The present invention relates to a thermoplastic processible aminoplast resin, a process for its production, a duroplastic fine fiber non-woven material, a process and an apparatus for the production of duroplastic fine fiber non-woven material from thermoplastic processible aminoplast resins, in particular melamine resins, and the use of the duroplastic fine fiber non-woven materials.
2) Description of the Prior Art
In different areas of the processing industry a high demand on fiber materials exists, which have to be chemical resistant, hardly inflammable, easy to process, producible to low costs and without danger for human and environment. Areas of application of such fiber materials are for instance protective clothing or the interior of vehicles and hotel furniture/soft furnishing for public buildings, where the requirements regarding resistance against flames are high, furthermore insulating material for engines or filter materials for industrial processes.
Duroplastic material on the basis of triazine resins, as for example melamine-formaldehyde-resin, are very well suited for the mentioned application and form a group of hardly inflammable, chemically resistant and low cost starting materials producible in large amounts.
A disadvantage in the production of fibers or foams, semi-finished products or moulding materials, as for instance coatings, laminated material, laminates, molding materials, for domestic use and the electrical industry from triazine resins is however their difficult processability in usual thermoplastic processing methods like extrusion, injection molding or blow molding since high molecular melamine resins are cross-linked and infusible.
Non-cross-linked lower molecular melamine resin precondensates have a melt viscosity being too low for these processing methods and can solely be processed as highly filled molding masses with long cycle times by curing of the products (Woebcken, W. Plastic-Handbook, Vol. 10 “Duroplastic”, publisher Carl Hanser, Munich 1988, page 266-274).
Fibers (EP 00 93 965 A1), foams (EP 00 17 671 A1) or coatings (WO 96/20239 A1) from melamine resins can only be produced starting from solutions of the melamine resin precondensates by curing during shaping due to the low melt viscosity of the melamine resin precondensates.
Furthermore, the volatile side products generate micro pores and cracks in the surface of the product during polycondensation of the aminoplast precondensates. Therefore, materials are formed, which have a reduced resistance in respect to environmental impacts.
DE 100 56 398 describes a triazine formaldehyde resin processible from the melt, which is produced in a laborious three-step process. The precuring occurs in this case at relatively high temperatures (160-200° C.) in an extruder, whereby an extensive precuring is caused and therefore a high softening point above 100° C., whereby in turn a narrow processing window is caused.
Fiber materials are producible from melamine resins according to known methods (DE 100 38 030, WO 2006/100041). In case of the production according to a method of DE 100 38 030—in contrast to the method described here, whereat non-woven materials are produced in a one-step process from etherified melamine resins (so called MER)—practically no textile fibers can be produced 100% of melamine resins from the staple fibers thus obtained. Therefore, the use of such melamine resin fibers in the mentioned application is restricted or demands further, usually flame resistant fibers for guaranteeing the required properties.
Technologies and methods of the textile fleece formation are essentially influenced by the tradition based on the application of natural fibers. Natural fibers are present as staple fibers, which are defined by length and fineness. Synthetical fibers from melamine resins according to the mentioned methods, which are more suitable as any natural fiber for the mentioned application due to their preferred chemical and physical properties, are processed by processing steps as for instance carding according to the methods known from the prior art, in order to produce a hairline or a textile fleece therefrom. These processing steps are complex, laborious and lead to an unsatisfied result, since damages of the fibers occur and usually for guaranteeing the processibility a combination with other kind of fibers is required.
In practice, for instance fibers on the basis of polyaramide (m- and p-aramide) are used what increases the complexity of the production and increases considerably the production costs of such textile fleeces. It would be in particular of large interest for the mentioned application to provide a fleece (“non-woven”) for application as heat and flame resistant barrier layer in protection cloths, insulating materials and textile filter materials.
A method for the production of duroplastic fine fiber non-woven material is described in WO 2006/100041. The non-woven material obtained by this method shows large advantages compared to fiber materials obtainable by different methods; however their properties are still further improvable. In particular, their flexibility, strength and stability during further processing to the final products have to be improved.